Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. Critical temperature is the temperature above which

Water will evaporate

Water will never evaporate

A gas will immediately liquefy

A gas will never liquefy

2. A bootstrap air cooling system has

One heat exchanger

Four heat exchangers

Three heat exchangers

Two heat exchangers

3. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Low

Any value

4. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

5 tons

40 tons

5. The boiling point of ammonia is

-30°C

-10.5°C

-33.3°C

-77.7°C

6. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

7. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Condenser

Absorber

Evaporator

8. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

9. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Positive

Zero

None of these

10. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

Page 2 of 4

11. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

9: 1

1: 3

1: 1

12. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

13. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

15 bar

30 bar

14. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Good electrical conductor

High risibility with oil

Low boiling point

15. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

16. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Condenser and receiver

Compressor and condenser

Receiver and evaporator

17. The freezing point of sulphur dioxide is

-77.7°C

-75.2°C

-135.8°C

-56.6°C

18. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Miniature sealed unit

Centrifugal

Axial

19. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

20. Most thermostatic expansion valves are set for a superheat of

5°C

20°C

15°C

10°C

Page 3 of 4

21. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Ericson

Stirling

Carnot

22. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

23. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Brine

Ammonia

Freon

24. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

25. The capillary tube, as an expansion device, is used in

All of these

Domestic refrigerators

Room air conditioners

Water coolers

26. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Detect liquid in vapour

Collect vapours

27. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

28. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Normal cooling

Sub-cooling or under-cooling

Super-cooling

29. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

30. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

Above critical temperature

Page 4 of 4

31. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

32. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

33. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always more than unity

Any one of the above

Always less than unity

34. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

2.33

3.33

1.33

35. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.67

0.4

0.6

36. Freon group of refrigerants are

Inflammable

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

37. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

38. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

39. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

40. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Carnot

Rankine

Reversed Carnot

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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